The present invention relates turbochargers for internal combustion engines, and, more particularly, to a turbocharger turbine having a scalloped turbine wheel.
A limiting factor in the performance of an internal combustion engine is the amount of combustion air that can be delivered to the intake manifold for combustion in the engine cylinders. Atmospheric pressure is often inadequate to supply the required amount of air for proper operation of an engine at high efficiency. Therefore, it is common practice to use an auxiliary system to supply additional air to the intake manifold.
An internal combustion engine may include one or more turbochargers for compressing air that is then supplied to the combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine, and at least one compressor driven by the turbine. The compressor receives air to be compressed, and supplies the compressed air to the combustion cylinders. The turbocharger supplies combustion air to the engine at a higher pressure and higher density than atmospheric pressure and ambient density. The turbocharger can be used to make up for a loss of power due to altitude, or to increase the power that can be obtained from an engine of a given displacement. thereby reducing the cost, weight and size of an engine for a given power output.
It is also common to use exhaust gas recirculation systems (EGR systems) for controlling the generation of undesirable pollutant gases and particulate matter in the operation of an internal combustion engine. EGR systems have proven particularly useful for on the road motor equipment. In a typical EGR system, exhaust gas byproducts are recirculated to the intake air supply of the internal combustion engine. The result is a decrease in the concentration of oxygen, which in turn lowers the maximum combustion temperature within the cylinder, and slows the chemical reaction of the combustion process, thereby decreasing the formation of nitrous oxides (NOx). Unburned hydrocarbons in the exhaust gases can be burned on reintroduction to the engine cylinder, further reducing the emission of exhaust gas byproducts.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is normally removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many applications, the exhaust gas is diverted directly from the exhaust manifold. In a divided exhaust manifold system, an EGR system may be designed to take exhaust gas from both sides of the divided manifold system, or from only one side of the divided manifold system. Using either approach decreases the exhaust flow available to operate the turbine of the turbocharger. An example of an internal combustion engine having an exhaust gas turbocharger and an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey).
To reduce stresses in a turbocharger turbine wheel to an acceptable level, it is known to remove some of the material in the turbine wheel, thereby reducing the rotating mass. One practice has been to remove material near the outer diameter of the turbine wheel, between the turbine blades. This practice is referred to as xe2x80x9cscallopingxe2x80x9d, as the outer edge of the turbine wheel will have a scalloped appearance. While the practice of scalloping has advantages in reducing turbine wheel stresses, turbine performance is reduced in that the scalloped wheel disrupts the smooth flow of exhaust gas through the turbine. In an engine having significant EGR flow, it is desirable to maintain turbine efficiency at a high level, to take advantage of the decreased exhaust gas flow available to the turbocharger, and thereby provide sufficient compressed air flow to the engine for combustion. The decrease in efficiency from the use of a scalloped turbine wheel may offset the advantages obtained from scalloping, particularly in an engine having significant EGR flow.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with a plurality of combustion cylinders, an exhaust manifold, an intake manifold and a turbocharger. The turbocharger includes a compressor having an inlet receiving combustion gas and an outlet in fluid flow communication with the intake manifold, and a turbine drivingly coupled to the compressor. The turbine has a turbine casing, a shaft rotatably disposed in the casing, and a turbine wheel disposed on the shaft in the casing. The turbine wheel has a plurality of turbine blades and an edge defining a plurality of scallops. Scallop fillers are disposed between the turbine blades.
In another aspect of the invention, a turbocharger is provided with a compressor having an inlet receiving combustion gas and an outlet; and a turbine drivingly coupled to the compressor. The turbine has a shaft and a turbine wheel disposed on the shaft. The turbine wheel has a plurality of turbine blades and an edge defining a plurality of scallops. Scallop fillers are disposed between the turbine blades.
In yet another aspect of the invention, a turbine is provided with a turbine casing, a shaft rotatably disposed in the casing and a turbine wheel disposed on the shaft. The turbine wheel has a plurality of turbine blades and an edge defining a plurality of scallops. Scallop fillers are disposed between the turbine blades.
In still another aspect of the invention, a method of operating an internal combustion engine, is provided, with steps of providing a plurality of combustion cylinders, an exhaust manifold and an intake manifold; transporting exhaust gas from the plurality of combustion cylinders to the exhaust manifold; providing a turbocharger including a compressor having an inlet and an outlet, and a turbine having an inlet and an outlet, a turbine wheel, a plurality of turbine blades and scallops on an outer edge of the turbine wheel; providing scallop fillers plugging the scallops; rotatably driving the turbine with exhaust gas introduced at the turbine inlet, flowing the exhaust gas along the turbine wheel and the scallop fillers to the turbine outlet; introducing combustion gas at the compressor inlet; and transporting combustion gas from the compressor outlet to the intake manifold.
In a further aspect of the invention, a turbine is provided with a turbine casing, a shaft rotatably disposed in the casing and a turbine wheel disposed on the shaft. The turbine wheel has a plurality of turbine blades and an outer edge. A means is provided, separate from and associated with the turbine wheel, for improving the aerodynamic efficiency of fluid flow along the turbine blades.